Images on electronic displays are derived from an array of small, picture elements known as pixels. In color displays, these pixels comprise three color elements that produce the primary colors, for example, red, blue and green (R, G and B). Usually arranged in rectangular arrays, these pixels can be characterized by a pixel pitch, P, a quantity that measures the spacing of pixels in one direction. A typical cathode-ray tube (CRT) display used for computer applications has a pixel pitch of 0.3 mm. Computer screens have a pixel array width:height ratio of 4:3. Typical, standardized arrays in computer displays are comprised of 640.times.480, or 1024.times.768 pixels.
Large displays can be constructed of a plurality of adjacent tiles, with each having a single pixel or an array thereof. Such assembled tiled displays contain visually disturbing seams, resulting from the gaps between adjacent pixels on the same and/or adjacent tiles. Such seams may incorporate interconnect adhesives, seals, mechanical alignment means and other components resulting in visible optical discontinuities in displayed images. Some of these structures are described in the aforementioned patent application Ser. No. 08/571,208. As a consequence, the image portrayed on seamed displays appears segmented and disjointed. Therefore, it is desirable to fabricate tiled, flat-panel displays which do not have noticeable or perceptible seams under the intended viewing conditions.
The pixel pitch in electronic displays must be set so that a continuous image is produced when the display is viewed at distances larger than the minimum viewing distance. For example, with a pixel pitch of P=0.3 mm, the minimum viewing distance is on the order of 1 m. Even though the minimum viewing distance increases in proportion to the pixel pitch, it still limits the pixel pitch for most computer and consumer displays. Since space for the tiling functions must be provided in spaces comparable in size to the pixel pitch, it is difficult to develop structures and methods for constructing tiled displays.
Flat-panel displays (FPD) provide the best choice for constructing "seamless", tiled screens. Flat-panel displays include backlighted and self-lighted displays. Liquid crystal displays (LCDs) are the most common backlighted displays. Flat-panel displays depend on the microfabrication of key components that carry the pixel patterns. Microfabrication techniques are not viable for large displays, due to the fact that the manufacturing yield declines rapidly with increasing area of the display. Therefore, the inventors have determined that small-sized tiles with arrays of pixels can be microfabricated and then assembled together to form a larger electronic display. Past attempts at accomplishing this have still resulted in visible seams, due in large part to the room that is required by tile assembling. The resulting pixel pitch at the edges of tiles was much larger than in the interior of the tiles. This is essentially the reason for the fact that there have only been a few, unsuccessful attempts made to fabricate the large, "seamless", tiled panels.
However, the present invention provides unique designs and methods for achieving such large, "seamless", tiled panels for color or gray-scale displays. This invention particularly focuses on displays of the transparent, lightvalve type. In such displays, light from a uniform, backlight source is transmitted through the display assembly and directly viewed from the front side of the display. The lightvalves control the amount of primary light rays transmitted through each of the color elements in the pixels. The viewer's eyes merge the primary light from the pixels to form a continuous image at a sufficient viewing distance. Because of a number of secondary processes, low-level light emanates from the spaces between the pixels. These phenomena include reflection and light guiding, all of which must be kept to a minimum in order to achieve sufficient brightness and contrast. The gaps between pixels on the same tile, and the gaps between pixels on adjacent tiles have different structures. Consequently, the presence of seams between the pixels at the edge of the tiles will affect both primary and secondary light rays, thus increasing the difficulties for constructing seamless, tiled displays.
The inventors have determined that there are three design principles in making large-scale, "seamless", flat panels that may be viewed as though they were single monolithic displays: (a) the pixel pitch on the tiles must be matched to that of the pixel pitch between the tiles; (b) the primary light paths through the lightvalves must not be affected by the presence of the seam or any other structures or components used in the tile assembly; (c) the inter-pixel gaps must be designed so that intra-tile and inter-tile pixel gaps, which have different physical structures, present approximately the same visual appearance to the viewer under transmitted and reflected light.